A little trick to disguise the taste of different water is to start adding a little mint flavor to it at home. That way when you are on the road, you can add the mint flavor to that water, and it will mask the different taste and make them more likely to drink it.
Chances are if you are away for a whole week, and he is stabled there, he will start to drink once he settles in. But flavoring the water should help out a bit.
"The white horse moved like a dancer, which is not surprising: a horse is a beautiful animal, but it is perhaps most remarkable because it moves as if it always hears music."